To date, there has been known an electric power steering apparatus that adds assist force to steering power in order to make a driver comfortably perform steering; the electric power steering apparatus is provided with a motor and a control apparatus for controlling the motor. When due to increase in the output, the motor is upsized, it is required to raise the strength and the vibration resistance of the system while securing the heat radiation performance; in addition, due to increase in the function, the number of electronic components increases; thus, it is also required to enlarge the mounting area for a control circuit. Moreover, for the purpose of achieving improvement of the gasoline mileage of a vehicle, taking an environmental issue into consideration, it is strongly required to downsize the system; Patent Documents 1 and 2 disclose structural technologies for coping with these issues.